Apparatus and method for depositing a semiconductor material

ABSTRACT

Apparatus (12, 12a) and a method for depositing a semiconductor material on a glass sheet substrate (G) utilizes a distributor (22) including a heated permeable member (24) through which a carrier gas and a semiconductor material are passed to provide a vapor that is deposited as a semiconductor layer on the conveyed glass sheet substrate. The permeable member (24) is tubular and has an electrical voltage applied along its length to provide the heating, and the carrier gas and the semiconductor as a powder are introduced into the tubular permeable member for flow outwardly therefrom as the vapor. A shroud (34) extending around the tubular permeable member (24) has an opening (36) through which the vapor flows for the semiconductor layer deposition. In one embodiment of apparatus (12), the semiconductor layer is deposited on an upwardly facing surface (56) of the glass sheet substrate (G) while another embodiment of the apparatus (12a) deposits the semiconductor layer on a downwardly facing surface (54) of the substrate.

TECHNICAL FIELD

This invention relates to apparatus and a method for depositing asemiconductor material on a glass sheet substrate.

BACKGROUND ART

The United States Patents of Foote et al. U.S. Pat. Nos. 5,248,349,5,372,646, 5,470,397 and 5,536,333, which are assigned to the assigneeof the present invention and the entire disclosure of which is herebyincorporated by reference, disclose a continuous process for depositionof semiconductor material as a layer of cadmium telluride on a glasssheet substrate. The Foote et al. patents disclose source materialtroughs in which the cadmium telluride is received within a processingchamber that is heated. Glass sheet substrates are conveyed below thesource material troughs such that sublimation of the source materialfrom the troughs produces deposition of the semiconductor material onthe upwardly facing surface of the conveyed glass sheets in a continuousmanner. This construction requires that the source material troughs beperiodically replenished with the cadmium telluride that provides thesemiconductor material. The Foote et al. patent also discloseintroduction of the source material as a vapor from sources of elementalcadmium and tellurium or from a source of cadmium telluride.

DISCLOSURE OF INVENTION

One object of the present invention is to provide improved apparatus fordepositing a semiconductor material on a glass sheet substrate.

In carrying out the above object, the apparatus of the inventionincludes a heated permeable member and also includes a material supplyfor supplying a carrier gas and the semiconductor material for flowthrough the heated permeable member and passage therefrom as a vapor. Aconveyor of the apparatus conveys a glass sheet substrate adjacent thepermeable member for deposition of the vapor on the substrate as asemiconductor layer.

The preferred construction of the apparatus has the heated permeablemember constructed with a tubular shape into which the material supplyintroduces the carrier gas and the semiconductor material for flowoutwardly therefrom as the vapor that is deposited on the glass sheetsubstrate as the semiconductor layer. This tubular permeable member hasopposite ends across which an electrical voltage is applied to provideits heating. Furthermore, the tubular permeable member is made ofsilicon carbide.

The preferred construction of the apparatus also includes a shroud of agenerally tubular shape that receives the tubular permeable member. Thisshroud has an opening through which the vapor passes for the depositionof the semiconductor layer on the glass sheet substrate. Mostpreferably, the opening of the shroud is a slit that extends along thetubular shape of the shroud. The shroud may have opposite ends betweenwhich the slit has a varying size to control the distribution of thevapor deposition onto the glass sheet substrate. Furthermore, the shroudis preferably made of a ceramic material that is disclosed as beingmullite.

As disclosed, the material supply introduces the carrier gas andsemiconductor material into one end of the tubular permeable member, andthe apparatus further includes another material supply that introducesthe carrier gas and the semiconductor material into the other end of thetubular permeable member.

Different embodiments of the apparatus are disclosed as including a gaspassage into which the semiconductor material is introduced as a powderfor flow with the carrier gas. Certain embodiments of the materialsupply include a rotary screw and the gas passage into which the rotaryscrew introduces the semiconductor material, with one of theseembodiments having the rotary screw rotating about a horizontal axis,and with another of these embodiments having the rotary screw rotatingabout a vertical axis. A further embodiment of the apparatus includes avibratory feeder and the gas passage into which the vibratory feederintroduces a powder of the semiconductor material for flow with thecarrier gas.

Each disclosed embodiment of the apparatus has the conveyor supportingthe glass sheet substrate in a horizontally extending orientation so asto have downwardly and upwardly facing surfaces. One embodiment of theapparatus has the heated permeable member located above the conveyor todeposit the semiconductor layer on the upwardly facing surface of theglass sheet substrate. In addition, that embodiment is disclosed asincluding rolls that support the downwardly facing surface of the glasssheet substrate. Another embodiment of the apparatus has the conveyorconstructed to include a gas hearth for supporting the glass sheetsubstrate in a generally horizontally extending orientation so as tohave downwardly and upwardly facing surfaces. The heated permeablemember of this latter embodiment is disclosed as being located below theglass sheet substrate to deposit the semiconductor layer on thedownwardly facing surface of the glass sheet substrate.

Another object of the present invention is to provide an improved methodfor depositing a semiconductor material on a glass sheet substrate.

In carrying out the immediately preceding object, the method fordepositing the semiconductor material is performed by heating apermeable member and by passing a carrier gas and a semiconductormaterial through the heated permeable member for heating to provide avapor. A glass sheet substrate is conveyed adjacent the heated permeablemember for deposition of the vapor on the glass sheet substrate as asemiconductor layer.

In the preferred practice of the method, an electrical voltage isapplied across opposite ends of the permeable member which has a tubularshape into which the carrier gas and the semiconductor material areintroduced for passage outwardly therethrough as the vapor that isdeposited on the glass sheet substrate as the semiconductor layer.

The vapor is guided around the exterior of the tubular permeable memberby a shroud and is passed outwardly through an opening in the shroud forthe deposition on the glass sheet substrate as the semiconductor layer.The vapor may be passed outwardly from the shroud through a slit-shapedopening having opposite ends between which the opening has a varyingsize to control distribution of the deposition of the vapor on the glasssheet substrate as the semiconductor layer. Furthermore, the carrier gasand the semiconductor material are disclosed as both being introducedinto opposite ends of the tubular permeable member.

Different practices of the method have the semiconductor materialintroduced as a powder into the carrier gas for flow to and through theheated permeable member. In one such practice of the method, thesemiconductor powder is introduced into the carrier gas by a rotaryscrew, while another such practice of the method introduces thesemiconductor powder into the carrier gas by a vibratory feeder.

As disclosed, the method is performed using a carrier gas that ishelium.

Two different practices of the method are both performed by conveyingthe glass sheet substrate in a horizontally extending orientation so asto have downwardly and upwardly facing surfaces, with the vapor flowingdownwardly for deposition of the semiconductor layer on the upwardlyfacing surface of the conveyed glass sheet substrate in one practice ofthe method, and with the vapor flowing upwardly for deposition of thesemiconductor layer on the downwardly facing surface of the conveyedglass sheet substrate in the other practice of the method.

The objects, features and advantages of the present invention arereadily apparent from the following detailed description of the bestmodes for carrying out the invention when taken in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic elevational view illustrating apparatus fordepositing a semiconductor material on a glass sheet substrate inaccordance with the present invention.

FIG. 2 is a partially broken-away sectional view taken through adistributor of the apparatus along the direction of line 2--2 in FIG. 1and illustrates a pair of material supplies for introducing a carriergas and a semiconductor material into opposite ends of a tubularpermeable member.

FIG. 3 is a sectional view through the distributor taken along thedirection of line 3--3 in FIG. 2.

FIG. 4 is a bottom plan view taken along the direction of line 4--4 ofFIG. 2 to illustrate a varying size slit opening of a shroud of theapparatus.

FIG. 5 is a view illustrating an alternate embodiment of the materialsupply which includes a rotary screw that rotates about a vertical axisas opposed to rotating about a horizontal axis as illustrated in FIG. 2.

FIG. 6 is a view of a further embodiment of the material supply whichincludes a vibratory feeder.

FIG. 7 is a view illustrating another embodiment where the semiconductormaterial is deposited on a downwardly facing surface of the conveyedglass sheet substrate as opposed to being deposited on an upwardlyfacing surface thereof as shown in FIG. 1.

BEST MODES FOR CARRYING OUT THE INVENTION

With reference to FIG. 1 of the drawings, a glass sheet processingsystem generally indicated by 10 includes apparatus 12 constructedaccording to the invention to perform the method of the invention. Boththe apparatus 12 and the method for processing glass sheets G accordingto the invention will be hereinafter more fully described in anintegrated manner to facilitate an understanding of the differentaspects of the invention.

With continuing reference to FIG. 1, the system 10 includes a housing 14defining a processing chamber 16 in which a semiconductor material isdeposited on glass sheet substrates G. Housing 14 includes an entrystation 18 and an exit station 20. These entry and exit stations 18 and20 can be constructed as load locks or as slit seals through which theglass sheet substrates G enter and exit the processing chamber 16. Thehousing 14 is heated in any suitable manner such as disclosed by theaforementioned Foote et al. patents such that its processing chamber ismaintained at a temperature of 500° to 700° C., and the glass sheetsubstrates are heated during the processing to a slightly lowertemperature of about 400° to 650° C.

With continuing reference to FIG. 1 and additional reference to FIGS. 2and 3, the apparatus 12 of the invention includes a distributor 22having an electrically conductive permeable member 24 of a tubular shapehaving an elongated construction. The tubular permeable member 24 isheated, which as disclosed is performed by electrical connections 26 atits opposite ends 28 and application of a voltage along the length ofthe member. This voltage causes an electrical current to flow along thelength of the tubular permeable member 24 so as to provide electricalheating thereof during the processing. This heating of the tubularpermeable member 24 is to a temperature of about 850° to 1150° C. Atleast one material supply 30 of the apparatus 12 is provided forintroducing a carrier gas and a semiconductor material into the tubularpermeable member 24 for heating to provide a vapor that passes outwardlythrough the tubular permeable member during the processing. A conveyor32 of the apparatus conveys a glass sheet substrate G adjacent thedistributor 22 for deposition of the vapor on the substrate as asemiconductor layer.

In the preferred construction of the apparatus 12, the tubular permeablemember 24 is made of silicon carbide although it could also be made ofpermeable carbon or any other permeable material that is preferablyelectrically conductive to provide the heating in the manner disclosed.Furthermore, the distributor 22 preferably includes a shroud 34 of agenerally tubular shape that receives the tubular permeable member 24 asbest illustrated in FIG. 3. The shroud 34 guides the vapor around theexterior of the tubular permeable member 24 and has an opening 36through which the vapor passes for the deposition of the semiconductorlayer on the glass sheet substrate G. More specifically, the preferredconstruction of the shroud 36 has the opening 36 constructed as a slitthat extends along the tubular shape of the shroud. The shroud 34 asshown in FIG. 4 has opposite ends 37 between which the slit-shapedopening 36 has a varying size which facilitates distribution of thevapor and uniform deposition of the semiconductor layer. Morespecifically, the slit-shaped opening 36 has a smaller size adjacent theends 37 where the carrier gas and semiconductor material are introduced,as is hereinafter more fully described, and has a larger size at thecentral more remote area from that introduction so as to provide theuniform deposition. To provide good distribution of the semiconductormaterial, it may be desirable to provide the interior of the tubularpermeable member 24 with a suitable diverter that provides a uniformpassage of the vapor outwardly along the length of the tubular permeablemember and then along the length of the slit-shaped opening 36 of theshroud. Furthermore, the shroud 34 is preferably made of a ceramicmaterial that is most preferably mullite.

The shroud 34 also advantageously reduces radiant heat transfer from thehot tubular permeable member 24 to the glass sheet substrate G. Morespecifically, the amount of energy the shroud 34 radiates to the glasssheet substrate is reduced because its outside surface temperature islower than that of the hot tubular permeable member 24. Mullite has anadequately low emissivity and is relatively strong and easy tofabricate. In addition, it should be appreciated that coatings can beprovided to lower the emissivity of the outer surface of the shroud 34such as Al₂ O₃ or Y₂ O₃.

It should also be noted that the length of the slit-shaped opening 36 ofthe shroud 34 can be selected to control the extent of the width of thedeposited layer on the glass sheet substrate. Thus, the length of thesplit-shaped opening 36 can be selected to be less than the width of theglass sheet substrate to provide a strip of the deposited layer. Suchcontrol can also minimize waste of the vapors. When the entire width ofthe substrate is to be covered, one can ideally make the length of theslit-shaped opening 36 equal to or slightly less than the width of thesubstrate such that the substantially all of the vapors are depositedonto the substrate during the deposition.

In providing efficient deposition, the shroud 34 has been spaced fromthe conveyed glass sheet substrate a distance in the range of 0.5 to 3.0centimeters. While greater spacings could be utilized, that wouldrequire lower system pressures and would result in vapor waste due tooverspraying. Furthermore, smaller spacing could cause problems due tothermal warpage of the glass sheet substrate during conveyance.

As illustrated in FIG. 2, the material supply 30 introduces a carriergas from a source 38 and a semiconductor material as a powder 40 from ahopper 42 into one end 28 of the tubular permeable member 24, and thereis also another material supply 30 that likewise introduces a carriergas and a semiconductor material as a powder into the other end 28 ofthe tubular permeable member 24. As such, there is a good distributionof the carrier gas and entrained semiconductor powder along the entirelength of the tubular permeable member 24.

With continuing reference to FIG. 2, each of the material supplies 30illustrated includes a rotary screw 44 that receives the semiconductorpowder 40 from the hopper 42 and is rotatively driven by a suitableactuator 46. A passage 48 extends from the carrier gas source 38 to theadjacent end 28 of the porous tubular member 24 in communication withthe rotary screw 44. Rotation of the screw 44 at a controlled rateintroduces the semiconductor powder 40 into the passage 48 so as to beentrained therein for flow into the tubular permeable member 24 for theheating that provides the vapor.

FIGS. 2, 5 and 6 respectively disclose different embodiments of thematerial supplies 30, 30' and 30". More specifically, the embodiment ofthe material supply 30 illustrated in FIG. 2 has the screw 44 rotatedabout a horizontal axis for introduction of the semiconductor powder 40into the carrier gas passage 48, while the FIG. 5 embodiment of thematerial supply 30' has the screw 44 rotated about a vertical axis forintroduction of the semiconductor powder 40 from the hopper 42 into thecarrier gas passage 48. With each of these screw embodiments of thematerial supplies, the amount of semiconductor material introduced as apowder can be accurately controlled by the rate of screw rotation.Furthermore, the FIG. 6 embodiment of the material supply 30" includes avibratory feeder 50 having an inclined passage 52 extending upwardlyfrom the hopper 42 to the carrier gas passage 48. Operation of thevibratory feeder 50 causes vibration of the semiconductor powder 40which moves it upwardly along the inclined passage 52 to the carrier gaspassage 48 for flow as an entrained powder into the tubular permeablemember 24.

It should be appreciated that other types of material supplies can alsobe utilized for feeding the semiconductor powder including fluidized bedfeeders and rotary disk feeders that are commercially available. Thepowder feed rate and the speed of conveyance of the glass sheetsubstrate directly control the film thickness such that the carrier gasflow rate, powder feed rate, and glass sheet conveyance speed all mustbe controlled. Also, starting and stopping of the powder feed can beutilized to commence and terminate the deposition of the semiconductorlayer on the glass sheet substrate.

Two different embodiments of the apparatus 12 and 12a respectivelyillustrated by FIGS. 1 and 7 both support the glass sheet substrate G ina horizontally extending orientation so as to have downwardly andupwardly facing surfaces 54 and 56.

In the embodiment of FIG. 1, the distributor 22 is located above theconveyor 32 so as to deposit the semiconductor layer on the upwardlyfacing surface 56 of the glass sheet substrate G. Furthermore, thisembodiment of the apparatus discloses the conveyor 32 as being of theroll type including rolls 58 that support the downwardly facing surface54 of the glass sheet substrate for its conveyance during theprocessing.

In the embodiment of FIG. 7, the apparatus 12a has the conveyor 32aconstructed as a gas hearth for supporting the glass sheet substrate Gfor conveyance. More specifically, the gas hearth conveyor 32a includesa refractory hearth 60 above a plenum 62 of heated pressurized gas.Holes 64 in the hearth 60 provide for the upward flow of the pressurizedheated gas so as to support the glass sheet substrate G in a floatingmanner. The hearth 60 in accordance with conventional construction canalso include exhaust openings through which the gas escapes backdownwardly through the hearth into a suitable return chamber that is notillustrated. In this gas hearth construction of the conveyor 32a, thedistributor 22 is located below the glass sheet substrate G to depositthe semiconductor layer on its downwardly facing surface 54. Thus, theopening 36 provided by the slit in the shroud 34 is at the upperextremity of the distributor 22 in this embodiment, unlike theembodiment of FIG. 1 where the slit opening 36 is at the lower extremityof the shroud.

It should also be appreciated that the gas hearth conveyor can beutilized with a distributor located above the conveyed glass sheetsubstrate so as to provide the deposition on its upper surface as in theembodiment of FIG. 1 and unlike the embodiment of FIG. 7 which providesthe deposition on the lower surface.

In performing the deposition, successful results have been achievedusing cadmium telluride and cadmium sulfide as the semiconductormaterial. However, it should be appreciated that other semiconductormaterials can be utilized including elements of Group IIB and Group VIA,as well as compounds including these elements, such as for example, zincselenide, etc. and other materials that become semiconductors uponfurther processing. Also, dopants may be useful to enhance thedeposition.

Use of the apparatus to perform the method of the invention has beenperformed with a vacuum drawn in the processing chamber 16 to about 1 to50 Torr. In that connection, as illustrated in FIG. 1, the processingsystem 10 includes a suitable exhaust pump 66 for exhausting theprocessing chamber 16 of the housing 14 both initially and continuouslythereafter to remove the carrier gas.

The carrier gas supplied from the source 38 is most preferably heliumwhich has been found to increase the glass temperature range and thepressure range that provide good semiconductor characteristics such asdense deposition and good bonding. The carrier gas can also be anothergas such as nitrogen, neon, argon or krypton, or combinations of thesegases. It is also possible for the carrier gas to include a reactive gassuch as oxygen that can advantageously affect growth properties of thesemiconductor material. A flow rate of 0.3 to 10 standard liters perminute of the carrier gas has been determined to be sufficient toprovide the semiconductor material flow to the distributor 22 for thedeposition.

While the best modes for carrying out the invention have been describedin detail, those familiar with the art to which the invention relateswill appreciate other ways of carrying out the invention as defined bythe following claims.

What is claimed is:
 1. Apparatus for depositing a semiconductor materialon a glass sheet substrate, comprising:a heated permeable member; amaterial supply for supplying a carrier gas and the semiconductormaterial for flow through the heated permeable member and passagetherefrom as a vapor; and a conveyor for conveying a glass sheetsubstrate adjacent the heated permeable member for deposition of thevapor on the substrate as a semiconductor layer.
 2. Apparatus fordepositing a semiconductor material as in claim 1 wherein the heatedpermeable member has a tubular shape into which the material supplyintroduces the carrier gas and the semiconductor material for flowoutwardly therefrom as the vapor that is deposited on the glass sheetsubstrate as the semiconductor layer.
 3. Apparatus for depositing asemiconductor material as in claim 2 wherein the tubular permeablemember has opposite ends across which an electric voltage is applied toprovide its heating.
 4. Apparatus for depositing a semiconductormaterial as in claim 3 wherein the tubular permeable member is made ofsilicon carbide.
 5. Apparatus for depositing a semiconductor material asin claims 2, 3 or 4 further including a shroud of a generally tubularshape that receives the tubular permeable member, and the shroud havingan opening through which the vapor passes for the deposition of thesemiconductor layer on the glass sheet substrate as the semiconductorlayer.
 6. Apparatus for depositing a semiconductor material as in claim5 wherein the opening of the shroud is a slit that extends along thetubular shape of the shroud.
 7. Apparatus for depositing a semiconductormaterial as in claim 6 wherein the shroud has opposite ends betweenwhich the slit has a varying size.
 8. Apparatus for depositing asemiconductor material as in claim 5 wherein the shroud is made of aceramic material.
 9. Apparatus for depositing a semiconductor materialas in claim 8 wherein the ceramic material is mullite.
 10. Apparatus fordepositing a semiconductor material as in claim 2 wherein the materialsupply introduces the carrier gas and semiconductor material into oneend of the tubular permeable member.
 11. Apparatus for depositing asemiconductor material as in claim 10 further including another materialsupply that introduces the carrier gas and the semiconductor materialinto the other end of the tubular permeable member.
 12. Apparatus fordepositing a semiconductor material as in claim 1 wherein the materialsupply includes a rotary screw and a gas passage into which the rotaryscrew introduces a powder of the semiconductor material for flow withthe carrier gas.
 13. Apparatus for depositing a semiconductor materialas in claim 12 wherein the rotary screw rotates about a horizontal axis.14. Apparatus for depositing a semiconductor material as in claim 12wherein the rotary screw rotates about a vertical axis.
 15. Apparatusfor depositing a semiconductor material as in claim 1 wherein thematerial supply includes a vibratory feeder and a gas passage into whichthe vibratory feeder introduces a powder of the semiconductor materialfor flow with the carrier gas.
 16. Apparatus for depositing asemiconductor material as in claim 1 or 3 wherein the conveyor supportsthe glass sheet substrate in a horizontally extending orientation so asto have downwardly and upwardly facing surfaces, and the heatedpermeable member being located above the conveyor to deposit thesemiconductor layer on the upwardly facing surface of the glass sheetsubstrate.
 17. Apparatus for depositing a semiconductor material as inclaim 16 wherein the conveyor includes rolls that support the downwardlyfacing surface of the glass sheet substrate.
 18. Apparatus fordepositing a semiconductor material as in claim 1 or 3 wherein theconveyor includes a gas hearth for supporting and conveying the glasssheet substrate in a generally horizontally extending orientation so asto have downwardly and upwardly facing surfaces.
 19. Apparatus fordepositing a semiconductor material as in claim 18 wherein the heatedpermeable member is located below the glass sheet substrate to depositthe semiconductor layer on the downwardly facing surface of the glasssheet substrate conveyed by the gas hearth.
 20. Apparatus for depositinga semiconductor material on a glass sheet substrate, comprising:adistributor including a tubular permeable member of silicon carbidehaving an elongated shape along which an electrical current flows toprovide heating; a pair of material supplies for introducing a carriergas and an entrained powder of a semiconductor material into oppositeends of the tubular permeable member for heating to provide a vapor thatpasses outwardly through the tubular permeable member; a shroud of atubular shape that receives the tubular permeable member, and the shroudhaving an opening formed as a slit through which the vapor passesoutwardly; and a conveyor for conveying a glass sheet substrate belowthe distributor for deposition of the vapor on the substrate as asemiconductor layer.
 21. A method for depositing a semiconductormaterial on a glass sheet substrate, comprising:heating a permeablemember; passing a carrier gas and a semiconductor material through theheated permeable member for heating to provide a vapor; and conveying aglass sheet substrate adjacent the heated permeable member fordeposition of the vapor on the glass sheet substrate as a semiconductorlayer.
 22. A method for depositing a semiconductor material as in claim21 wherein an electrical voltage is applied across opposite ends of thepermeable member which has a tubular shape into which the carrier gasand the semiconductor material are introduced for passage is outwardlytherefrom as the vapor that is deposited on the glass sheet substrate asthe semiconductor layer.
 23. A method for depositing a semiconductormaterial as in claim 22 wherein the vapor is guided around the exteriorof the tubular permeable member by a shroud and is passed outwardlythrough an opening in the shroud for the deposition on the glass sheetsubstrate as the semiconductor layer.
 24. A method for depositing asemiconductor material as in claim 23 wherein the vapor is passedoutwardly from the shroud through a slit-shaped opening having oppositeends between which the opening has a varying size.
 25. A method fordepositing a semiconductor material as in claim 23 wherein the carriergas and semiconductor material are both introduced into opposite ends ofthe tubular permeable member.
 26. A method for depositing asemiconductor material as in claim 21 wherein the semiconductor materialis introduced as a powder into the carrier gas for flow to and throughthe heated permeable member.
 27. A method for depositing a semiconductormaterial as in claim 26 wherein the semiconductor powder is introducedinto the carrier gas by a rotary screw.
 28. A method for depositing asemiconductor material as in claim 26 wherein the semiconductor powderis introduced into the carrier gas by a vibratory feeder.
 29. A methodfor depositing a semiconductor material as in claim 21, 22, 23 or 24wherein the carrier gas is helium.
 30. A method for depositing asemiconductor material as in claim 21, 22, 23 or 24 wherein the glasssheet substrate is conveyed in a horizontally extending orientation soas to have downwardly and upwardly facing surfaces.
 31. A method fordepositing a semiconductor material as in claim 30 wherein the vaporflows downwardly for deposition of the semiconductor layer on theupwardly facing surface of the conveyed glass sheet substrate.
 32. Amethod for depositing a semiconductor material as in claim 21, 22, 23 or24 wherein the glass sheet substrate is conveyed by a gas hearth in agenerally horizontally extending orientation so as to have upwardly anddownwardly extending surfaces, and the vapor flowing upwardly fordeposition of the semiconductor layer on the downwardly facing surfaceof the conveyed glass sheet substrate.